/*
 * Copyright (C) 2007-2016 Artima, Inc. All rights reserved.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *     http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * Example code from:
 *
 * Programming in Scala, Third Edition
 * by Martin Odersky, Lex Spoon, Bill Venners
 *
 * http://booksites.artima.com/programming_in_scala_3ed
 */

object Queues4 {
  class Queue[T] private (
    private val leading: List[T],
    private val trailing: List[T]
  ) 
  {
    private def mirror = 
      if (leading.isEmpty) new Queue(trailing.reverse, Nil)
      else this
    def head = 
      mirror.leading.head
    def tail = { 
      val q = mirror; 
      new Queue(q.leading.tail, q.trailing) 
    }
    def append(x: T) = 
      new Queue(leading, x :: trailing)

    override def toString() =
      (leading ::: trailing.reverse) mkString ("Queue(", ", ", ")")
  }


  object Queue {
    // constructs a queue with initial elements `xs'
    def apply[T](xs: T*) = new Queue[T](xs.toList, Nil)
  }

  def main(args: Array[String]) {
    val q = Queue[Int]() append 1 append 2
    println(q)
  }
}
